Laser marking device

ABSTRACT

A laser marking device for forming the pattern printed on a liquid crystal mask on the surface of an object. In the laser marking device, an input optical system (20) and an output optical system (30) are positioned on the input surface side of a reflective liquid crystal element (5) on which the laser beam (L) is made to fall through the input optical system (20). The angle of incident of the laser beam (L) on the input surface of the element (5) is approximately 90°. The laser beam (L) reflected by the element (5) is directed to the object (15) through the optical system (30). A cooling means (17) which cools the element (5) is provided in contact with the surface of the element (5) opposite to the surface which the laser beam strikes. In such a way, the space for the optical systems (20) and (30) is reduced. The space occupied by the cooling means (17) is reduced and the cooling efficiency and cooling uniformity of the means (17) are improved because the means (17) is in direct contact with the element (5).

TECHNICAL FIELD

The present invention relates to a laser marking device for marking amarking pattern of a liquid-crystal mask onto the surface of an objectwhich is to be marked.

BACKGROUND ART

A laser marking device which employs laser beams as a light source andliquid-crystal elements as printing pattern masks has already beenproposed in Japanese Patent Application Laid-open No.60-174671.

In laser marking devices of this kind, the incident face of aliquid-crystal mask is irradiated via an irradiating optical system withlaser beams which have been generated by a laser light source. Laserbeams which permeate the liquid-crystal mask are emitted from the faceopposite to the incident face.

For this reason, it is sought to prevent the optical system comprisingthe incident and emitting optical systems from spreading spatially tothe right and left. This is achieved either by locating the emittingoptical system, which guides emitted laser beams on to the object whichis to be marked, on the opposite side of the liquid-crystal mask to theincident optical system, or by employing a plurality of optical elementsdesigned to deflect the light emitted from the liquid-crystal mask tothe side on which the incident optical system is located.

Whichever of these methods was adopted, the optical system comprisingthe incident and emitting optical systems required a great deal of spacein both the horizontal and vertical directions.

In particular, the method which employs a plurality of optical elementsin order to deflect the light emitted from the liquid-crystal mask tothe side on which the incident optical system is located requiresmirrors, prisms and numerous other optical elements, with the resultthat it is costly.

Moreover, in order to prevent uneven marking it is necessary to ensurethat the liquid-crystal mask is not marred by unevenness of temperatureamong the pixels of the liquid-crystal screen. In view of the fact thatit takes longer to alter the liquid-crystal display if the temperatureis too low, and the contrast deteriorates if it is too high, it is clearthat there is an optimal temperature for the liquid-crystal mask.Consequently, the liquid crystal mask must be cooled so that theincident face is more even in temperature than the rear face, and so asto ensure that the optimal temperature is maintained.

In the case of conventional laser marking devices it has not beenpossible to locate a means of cooling in direct contact with theliquid-crystal mask face because they are configured in such a mannerthat the laser beam is incident on one face of the liquid-crystal mask,permeates it, and is emitted from the other face.

It has thus only been possible to cool it indirectly with a cooling fanor similar device using air as a medium. This method is problematic notonly on account of the space required for the cooling device, butbecause of a lack of uniformity in cooling efficiency.

It is a first object of the present invention, which has been designedwith these circumstances in mind, to save space for the optical systemcomprising the incident and emitting optical systems, and to lower costsby reducing the number of optical elements.

It is a second object of the present to make it possible for a means ofcooling to be brought into direct contact with the liquid-crystalelement, thus improving the efficiency and uniformity of cooling.

DISCLOSURE OF THE INVENTION

As has been explained above, it is a first object of the presentinvention to save space for the optical system comprising the incidentand emitting optical systems, and to lower costs by reducing the numberof optical elements. This first object is achieved by means of a firstinvention as described below.

In other words, the first invention is a laser marking device formarking printed patterns of a liquid-crystal mask onto the face of anobject which is to be marked by irradiating the liquid-crystal mask viaan incident optical system with a laser beam which has been generated bya laser light source, and guiding the laser beam which is emitted afterpermeating the liquid-crystal mask via an emitting optical system to theobject which is to be marked, wherein a reflective liquid-crystalelement is used as the liquid-crystal mask; and the incident opticalsystem and the emitting optical system whereby the laser beam which isemitted after permeating the reflective liquid-crystal element is guidedto the object which is to be marked are located on the incident faceside of the reflective liquid-crystal element, in such a manner that theoptical axis of the laser beam which is incident upon the reflectiveliquid-crystal element by way of the incident optical system is roughlyvertical in relation to the incident face of the reflectiveliquid-crystal element.

As FIG. 1 shows, the configuration of the first invention locates boththe incident optical system 20 and the emitting optical system 30 on theside of that face of the reflective liquid-crystal element 5 on whichthe laser beam L is incident. In addition, it allows the laser beam L tobe incident via the incident optical system 20 upon the reflectiveliquid-crystal element 5 in such a manner that the optical axis of thelaser beam L is roughly vertical in relation to the incident face of thereflective liquid-crystal element 5. Having been reflected by thereflective liquid-crystal element 5, the laser beam L is guided to theobject which is to be marked 15.

In this way, it is possible to inhibit the spatial expansion of theoptical system in the right-and-left direction because the incidentoptical system 20 and the emitting optical system 30 are located enmasse on the incident face side of the reflective liquid-crystal element5. It is also possible to inhibit the spatial expansion of the opticalsystem in the up-and-down direction because the optical system islocated in such a manner that the optical Axis of the laser beam L isroughly vertical in relation to the incident face of the reflectiveliquid-crystal element 5.

It is a second object of the present invention to make it possible tobring a means of cooling into direct contact with the liquid-crystalelement, thus conserving space and improving efficiency and uniformityof cooling.

This second object is achieved by means of a second invention asdescribed below.

In other words, the second invention is a laser marking deviceconfigured as described in the first invention, wherein a means ofcooling the reflective liquid-crystal element is located in contact withthe opposite face of the reflective liquid-crystal element to theincident face.

As FIG. 1 shows, the configuration of the second invention locates boththe incident optical system 20 and the emitting optical system 30concentratedly on the incident face side of the reflectiveliquid-crystal element 5, so that no optical elements are any longerlocated on the side of the opposite face of the reflectiveliquid-crystal element 5 to the incident face. It therefore becomespossible to bring a coling means 17 for cooling the reflectiveliquid-crystal element 5 into contact with the opposite face of thereflective liquid-crystal element 5 to the incident face.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the configuration of an embodiment of the lasermarking device to which the present invention pertains;

FIG. 2 illustrates another embodiment;

FIG. 3 shows the configuration of a reflective liquid-crystal elementwhich is used in the embodiments illustrated in FIGS. 1 and 2;

FIG. 4 (a) shows the configuration of a reflective liquid-crystalelement which is used in the embodiments illustrated in FIGS. 1 and 2,while FIG. 4 (b) is an enlarged drawing of section A of FIG. 4 (a); and

FIG. 5 shows the configuration of a reflective liquid-crystal elementwhich is used in the embodiments illustrated in FIGS. 1 and 2.

BEST MODE FOR CARRYING OUT THE INVENTION

There follows, with reference to the attached drawings, a detaileddescription of an embodiment of the laser marking device to which thepresent invention pertains.

As FIG. 1 shows, the laser marking device to which the embodiment referscomprises in the main a reflective liquid-crystal element 5, being aliquid-crystal mask for displaying a printed pattern which is to bemarked, an incident optical system 20 which causes a laser beam Lgenerated by a YAG laser oscillator 1 with a Q switch to be incidentupon the incident face of the reflective liquid-crystal element 5 at aninclination of a prescribed minute angle δto a vertical axis of theincident face, and an emitting optical system 30 whereby the laser beamL reflected by the reflective liquid-crystal element 5 is made toirradiate a marking face 15a of an object 15 which is to be marked.

In other words, what happens first is that data on the original imagewhich is to be marked on to the marking face 15a of the work 15 isrelayed from an external CPU (higher computer) to an internal controlunit of the laser marking device, and stored in a memory. That is tosay, the internal control unit stores a code number which refers to theoriginal image fed from the external CPU.

The YAG laser oscillator 1 is switched on when an oscillation startbutton of the control panel is pressed, and it begins oscillatingcontinuously. The laser beam L is not directed on to the reflectiveliquid-crystal element 5 unless the Q switch is in operation.

An example of the reflective liquid-crystal element 5 is ahigh-molecular complex liquid crystal, each pixel (dot) of the liquidcrystal being driven by electrical voltage.

In other words, the liquid crystal 5 has the property to reflect lightin the part of the pixels (dots) to which voltage has been imparted, andscatter the light in the part of the pixels to which no voltage has beenimparted so as not to reflect the light. There may be cases where eachpixel of the liquid crystal 5 is driven in a time division manner or isstatic-driven.

The reflective liquid-crystal element 5 comprises a liquid-crystal unit6 and a mirror unit 7. Light is reflected by the mirror unit 7. Theinternal configuration of the reflective liquid-crystal element 5 willbe described later.

When the marking start button is depressed, a motor which drives apolygonal mirror 2 and a scanning mirror 3 is driven to its initialposition by the internal control unit, and the initial setting of themotor and the initial setting of the reflective liquid-crystal element 5are performed. While the initial settings are being performed,processing is implemented by the internal control unit whereby theoriginal image stored in the abovementioned memory is partitioned, andprinting pattern data for the partitioned image which is to be displayedis fed to the reflective liquid-crystal element 5.

In other words, the internal control unit implements the process ofconverting the code numbers which represent the original image into codenumbers for each of the partitioned images, further converting thesecode numbers into an electrode applied signal to be applied to theelectrodes of the reflective liquid-crystal element 5. This signal isimparted to the reflective liquid-crystal element 5.

Once the initial setting of the motor and the reflective liquid-crystalelement 5 has been completed, the reflective liquid-crystal element 5 isswitched on, and each pixel of the reflective liquid-crystal element 5is driven by the electrode applied signals imparted to thereflective-type liquid-crystal element in the time division manner andthe partitioned image is displayed on the reflective liquid-crystalelement 5. The motor is driven, and scanning of the reflectiveliquid-crystal element 5 commences.

Once the reflectivity of the displayed and non-displayed pixels of thereflective liquid-crystal element 5 has stabilized, the internal controlunit imparts a trigger signal to the Q switch of the YAG laseroscillator 1. The YAG laser oscillator 1 begins to generate pulses at apre-set frequency, causing the laser beam L to irradiate the incidentface of the reflective liquid-crystal element 5.

In other words, the laser beam L which is output from the YAG laseroscillator 1 is pinpointed on to the incident face of the reflectiveliquid-crystal element 5 by way of the polygon mirror 2, scanner mirror3 and a wide-diameter field lens 4 which is located directly in front ofthe incident face of the reflective liquid-crystal element 5. The fieldlens 4 is an optical element which serves to render the optical axis ofthe incident laser beam L vertical in relation to the incident face ofthe reflective liquid-crystal element 5.

The internal control unit controls the rotation of the polygonal mirror2 and scan mirror 3, and raster-scans in order to ensure that the laserbeam L irradiates all parts of the pixels in the reflectiveliquid-crystal element 5.

The laser beam L reflected by a mirror unit 7 of the reflectiveliquid-crystal element 5 is emitted from the field lens 4 with anemitting optical axis which is symmetrical with the incident opticalaxis in relation to the vertical axis of the reflective liquid-crystalelement 5. The emitted laser beam L is guided through a field-correctionlens 8 in order to correct the distortion caused by the field lens 4,then through a mirror 9 which serves to deflect it in the X direction,an X-direction relay lens 10, a mirror 11, a Y-direction relay lens 12,a mirror 13 which serves to deflect it in the Y direction, and animage-formation lens 14 to the marking face 15a of the work 15, where aprinted pattern of the partitioned image (similar in shape to theprinted pattern which was displayed by the reflective liquid-crystalelement 5) is marked.

When marking of one partitioned image pattern is complete, initialsetting of the motor and reflective liquid-crystal element 5 isperformed in the same way as described above in preparation for markingthe next partitioned image. Marking pattern data for the nextpartitioned image which is to be displayed is fed to the reflectiveliquid-crystal element 5, and is marked on to the marking face 15a ofthe work 15 by raster-scanning the reflective liquid-crystal element 5in the same way.

When proceeding from the marking of the printed pattern of onepartitioned image to that of another, the rotational axis 9a of themirror 9 which serves to deflect the beam in the X direction and therotational axis 13a of the mirror 13 which serves to deflect it in the Ydirection are driven a certain distance, as shown by the arrows, inaccordance with the position in which the next partitioned image printedpattern is to be printed.

Thus, printed patterns of the partitioned image are marked one by one inthe corresponding coordinate positions (X, Y) on to the two-dimensionalX-Y plane of the marking face 15a of the work 15, so that ultimately aprinted pattern of the original image is marked.

The Q switch of the YAG laser oscillator 1 continues to operate once ithas been initiated, thus providing continuous laser-beam irradiation ofthe reflective liquid-crystal element 5.

With reference to FIG. 2, there now follows a description of anembodiment without scanning on the surface of the liquid crystal. Codeswhich are the same as those in FIG. 1 represent the same functions, andan explanation of them will be omitted here. Only the points ofdifference will be described.

In the incident optical system 20' illustrated in FIG. 2, the place ofan optical element for scanning the laser beam L is taken by a lens 16which serves to shape and expand the cross-section of a laser beam Lgenerated by a pulse-type laser oscillator 1' in accordance with theincident face of the reflective liquid-crystal element 5.

Having passed through this lens 16, the laser beam L is incident on thewhole of the incident face of the reflective liquid-crystal element 5,and all the pixel is irradiated en bloc.

Since the printed patterns of each partitioned image are displayed oneafter another on the reflective liquid-crystal element 5, and wholepixels are irradiated en bloc, marking is implemented without the needfor scanning by partitioned image as required in the embodimentillustrated in FIG. 1.

In the embodiments illustrated in both FIG. 1 and FIG. 2 provision ismade for a field-correction lens 8 to correct the field lens 4, but thismay be omitted if distortion presents no problem.

Similarly, in the embodiments illustrated in both FIG. 1 and FIG. 2provision is made for a field lens 4, but this itself may be omitted ifno problem is presented by the laser beam L not being verticallyincident on the incident face of the reflective liquid-crystal element5.

In this way, the embodiments illustrated in FIGS. 1 and 2 make itpossible to inhibit the spatial expansion of the optical system in thehorizontal direction by locating the incident optical system 20 or 20'and the emitting optical system 30 en masse on the incident face side ofthe reflective liquid-crystal element 5. They also make it possible toinhibit the spatial expansion of the optical system in the verticaldirection by locating it in such a manner that the optical axis of thelaser beam L is roughly vertical in relation to the incident face of thereflective liquid-crystal element 5.

Moreover, the fact that the reflective liquid-crystal element 5 itselfhas the function of causing the incident laser beam L to be reflected inthe original direction means that there is no longer any need for theseparate provision of an optical element designed to deflect theincident laser beam L in the original direction, thus reducing costs.

Thus, the abovementioned embodiments permit conservation of space andreduction of cost of the optical system.

Moreover, the fact that in the embodiments illustrated in FIGS. 1 and 2the incident optical system 20 or 20' and the emitting optical system 30are located en masse on the incident face side of the reflectiveliquid-crystal element 5 means that there are no longer any opticalelements located on the opposite face. This makes it possible to locatea means of cooling 17 (eg a heat sink or Peltier cooling element) incontact the face on the opposite side of the reflective liquid-crystalelement 5 from the incident face.

The fact that it is possible to employ a contact-type means of cooling17 not only makes it possible to conserve space, but represents aconsiderable improvement in terms of efficient and uniform cooling.

It is also necessary to control the reflective liquid-crystal element 5so as to maintain it at the prescribed optimal temperature.

Moreover, with a view to stabilizing the print quality, it is necessaryfor the reflectivity of the reflective liquid-crystal element 5 to bemaintained at the prescribed value.

In FIG. 1, a controller 40 is provided in order to execute this kind ofcontrol.

In other words, a laser beam from a laser beam source 41 is incidentupon the incident face of the reflective liquid-crystal element 5 forthe purpose of measurement. This laser beam is reflected by thereflective liquid-crystal element 5 and detected by a photosensor 42.

The controller 40 imparts a drive command signal V1 to the laser beamsource 41 in order to ensure that the laser beam generated by the laserbeam source 41 is always of a constant power. The photosensor 41 detectsthe power of the reflected laser beam, and a detection signal S1 isinput into the controller 40.

The controller 40 measures the degree of reflectivity from the size ofthe detection signal S1. If the reflectivity is found to be too low, itimparts a drive command signal V3 to the reflective liquid-crystalelement 5, so that its drive voltage can be increased, thus improvingthe reflectivity. If on the other hand the reflectivity is found to betoo high, a drive command signal V3 is imparted to the reflectiveliquid-crystal element 5, so that its drive voltage can be decreased,thus reducing the reflectivity. In this way the reflectivity of thereflective liquid-crystal element 5 is maintained at the prescribedtarget level.

Temperature control is implemented by means of a temperature sensor 43which is located on the opposite side of the reflective liquid-crystalelement 5 to the incident face. This temperature sensor 43 detects thetemperature S2 of the liquid crystal, which is then input into thecontroller 40. The controller 40 outputs a drive command signal V2 tothe means of cooling 17 and controls temperature feedback, using thetemperature S2 detected by the above-mentioned temperature sensor 43 asthe degree of feedback to attain the prescribed target temperature.

The same control process is also present in FIG. 2, although it is notshown.

In the embodiments it has been assumed that the lasers are YAG lasers,but this does not mean that they are restricted to these, and it is alsopossible to utilize semiconductor lasers, argon lasers and other typesof laser.

In the embodiments it has also been assumed that the liquid crystalelement which is used as the reflective liquid-crystal element is suchthat increasing the drive voltage will improve its reflectivity, butthis does not mean that it is restricted in this way, and it is alsopossible to use one where decreasing the drive voltage has that effect.

There now follows a description of the internal structure of thereflective liquid-crystal element 5 with reference to FIGS. 3, 4 and 5.

In FIG. 3, the whole of the face on the opposite side to the incidentface of the liquid-crystal unit 6 is has been given a reflective coating7', consisting of a single layer of film or a plurality of layers oflaminated film. This reflective coating 7' allows the laser beam L to bereflected.

An example of a material which may be used for this reflective coatingis metal film, but it is also possible to employ other substances asdesired, provided that they have the property of reflecting incidentlaser beams. By selecting the prescribed thickness it is also possibleto use transparent films which have the property of reflecting incidentlaser beams.

In FIG. 4 (a), the reflective liquid-crystal element 5 is configured insuch a manner that a liquid crystal is sandwiched between two sheets ofglass 6a, 6b. That is to say, the enlarged section A shown in FIG. 4 (b)is configured in such a manner as to give, in order from the side onwhich the laser beam is incident, a sheet of glass 6a, a film comprisingan electrically conductive material 6d, a liquid crystal 6c, a filmcomprising an electrically conductive material with total reflectivefunction 6e, and a sheet of glass 6b. Here, the laser beam L is causedto be reflected by imparting a total reflective function to the filmcomprising an electrically conductive material 6e. This function can beachieved, for instance, by selecting a prescribed thickness of film.FIG. 5 shows a reflective liquid-crystal element 5 wherein a liquidcrystal is sandwiched in the same way between two sheets of glass 6a,6b.

In this case, the interface B between the liquid crystal 6c and the filmof electrically conductive material 6d on the side opposite to that onwhich the laser beam is incident, or the interface C between the samefilm of electrically conductive material 6d and the glass 6d has beengiven a reflective coating consisting of a single layer of film or aplurality of layers of laminated film. These sections with reflectivecoating B, C allow the laser beam L to be reflected.

An example of a material which may be used for this reflective costingis metal film, but it is also possible to employ other substances asdesired, provided that they have the property of reflecting incidentlaser beams. By selecting the prescribed, thickness it is also possibleto use transparent films which have the property of reflecting incidentlaser beams.

As has been explained above, the present invention makes it possible toconserve space in the incident and emitting optical systems in a lasermarking device. It also allows costs to be reduced because there is noneed for an optical element in order to deflect the laser beam.

Moreover, it becomes possible to locate a means of cooling in contactwith the opposite face of the reflective liquid-crystal element to theincident face, thus making it possible not only to conserve the spacerequired for providing a means of cooling, but considerably improvingthe efficacy and uniformity of cooling.

We claim:
 1. A laser marking device for marking printed patterns of aliquid-crystal mask on to a surface of an objection which is to bemarked by irradiating the liquid-crystal mask via an incident opticalsystem with a laser beam which has been generated by a laser lightsource, and guiding the laser beam which is emitted after permeating theliquid-crystal mask via an emitting optical system to the object whichis to be marked, wherein a reflective liquid-crystal element is used asthe liquid-crystal mask; andthe incident optical system and the emittingoptical system whereby the laser beam which is emitted after permeatingthe reflective liquid-crystal element is guided to the object which isto be marked are located on an incident face side of the reflectiveliquid-crystal element, in such a manner that an optical axis of thelaser beam which is incident upon the reflective liquid-crystal elementby the incident optical system is roughly vertical in relation to theincident face of the reflective liquid-crystal element.
 2. The lasermarking device as described in claim 1, wherein means of cooling thereflective liquid-crystal element is located in contact with an oppositeface of the reflective liquid-crystal element to the incident face. 3.The laser marking device as described in claim 1, wherein the reflectiveliquid-crystal element is a high-molecular complex liquid crystal. 4.The laser marking device as described in claim 1, wherein the reflectiveliquid-crystal element is structured by applying a total reflectivecoating to an opposite face of the liquid-crystal element to theincident face.
 5. The laser marking device as described in claim 1,wherein the reflective liquid-crystal element is structured by endowinga film of electrically conductive material which constitutes theliquid-crystal element with a function whereby it reflects the laserbeam.
 6. The laser marking device as described in claim 1, wherein thereflective liquid-crystal element is structured by having a laser beamreflective film located in contact with a film of electricallyconductive material which constitutes the liquid-crystal element.